Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Co-Chair: Hertel, Nolan; Committee Co-Chair: Kahn, Bernd; Committee Member: Kulp, David; Committee Member: Lee, Eva; Committee Member: Wang, Chris. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Source: Dissertation Abstracts International, Volume: 54-08, Section: B, page: 3941. Supervisor: Robert J. Hardy. Includes bibliographical references (leaves 109-114).

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The method of measuring the energy of a charged particle by means of the total amount of ionisation it produces in a gas, through which it passes, is well established. Gas filled devices may be subdivided into (a) current ionisation chambers and (b) pulse ionisation chambers, proportional counters and Geiger counters. Proportional counters in a very crude form were used by Rutherford and Geiger in 1908. Soon afterwards the Geiger counter was developed, which after considerable improvement by Geiger and Müller in 1928, became the well known Geiger-Müller counter. In fact the three gas filled devices mentioned in (b) can be achieved with the same counter by using it with different applied voltages. If the applied voltage on a typical cylindrical counter is varied and the output pulse height is measured for a fixed number of ion pairs liberated in the gas, a characteristic curve of the form shown in Fig.(1) will be obtained. With voltages between say v₁ and v₂, the field strength is just sufficient to collect all the ion-pairs and no new ion-pairs are liberated, so the pulse height will remain constant. This is the region of pulse ionization chambers where the gas gain is unity. As the voltage is further increased to between v₂ and v₃ both elastic and inelastic collisions take place and the pulse height increases exponentially.

"Ouvrages à consulter": p. (220).

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This study has examined how the attainment of theoretical frameworks may create the conditions for and support subsequent learning of related material. In this regard, it has investigated a particular conception of Vygotsky‟s proposal that learning only occurs in the zone of proximal development, which he defined as the gap between what can be performed independently and what can be achieved with assistance. Specifically, it used a multi-pronged, mixed method research approach to probe the relationship between the actual level of development, as reflected by an ability to do proportional reasoning, and potential development, which was measured as the ability to perform certain strategic procedural operations in the molecular biosciences which were underpinned by proportionality. This four phase study which was carried out on a class of 106 second year students registered for Basic Molecular Biosciences II in the School of Molecular and Cell Biology, at the University of the Witwatersrand, Johannesburg, South Africa, initially measured proportional reasoning ability by posing a generative question requiring proportional reasoning to the class during a lecture and established that only 49% of the students who participated were able to answer the question. It could be shown statistically that these students were more adept at answering a contextual question based on proportion than those who had answered the generative question incorrectly, which suggested that actual development created the conditions for future learning. A paper and pencil test developed from Fleener (1993) which claimed to measure the hierarchical development of proportional reasoning ability was administered to the class and was used to select two groups for comparative purposes. The first group (group one) was comprised of the 23 students who scored 50 % or less, and the control group (group two) consisted of the 15 students who scored 100 %. Using these two groups, it was shown that the control group performed better than group one on specific questions underpinned by proportion which had been included in pre-laboratory tests and in summative assessments. Moreover, the control group‟s general performance in the course, as assessed by their marks in the examination at the end of the first semester, was substantially better than that of group one (67 % as opposed to a 51% average mark). These results were supported by findings where conceptual development of proportion had been judged from student‟s informal written accounts of the concept. Drawing on biological evidence, it was concluded that the actual level produces the structures necessary for further development. The second phase of the study utilized two focus groups constituted from students who iv had been randomly selected from the two groups compared in phase one of the research. Facilitated guided informal discussions probed which of factors like play and leisure activities, early childhood enrichment, schooling, mathematical ability and practices, instruction in proportional reasoning, and parental involvement, might have augmented the development of proportional reasoning ability. In phase three, the factors which emerged from the discussions were interrogated in a specially designed questionnaire which was administered to a sub-set of students who were concurrently registered for Basic Molecular Biosciences II and Biochemistry and Cell Biology II. Statistical analysis of the questionnaire which occurred in phase four of the research led to the conclusion that enrichment in early childhood, and having learnt proportion at school were the two factors that contributed most to attainment of the actual level of development which would enable subsequent learning of more elaborate procedural knowledge constructs based on the concept of proportion. These results supported the view that mediation results in internalisation of the embedded knowledge which can be drawn on for further learning in that domain. Therefore, in the final analysis of the research, it was concluded that actual levels of development create conditions for potential development as conceived by Vygotsky‟s zone of proximal development.

Este trabalho foi realizado com o objetivo de se estudar: - a concordância de um mesmo pesquisador, ao classificar, em ocasiões diferentes, as curvas de mortalidade proporcional, - a concordância entre diferentes pesquisadores na interpretação das curvas de mortalidade proporcional e ou - a concordância entre a curva de mortalidade proporcional e cada um dos indicadores, coeficiente de mortalidade infantil e razão de mortalidade proporcional, na indicação de alteração do nível de saúde de coletividades. Empreqou-se a estatística do tipo Kappa e encontrou-se: (GRÁFICO) / This study was realized with the purpose of examining: - the agreement of the same researcher, in classifying, on different occasions, the proportional mortality curves, - the agreement among different researchers in the interpretation of the proportional mortality curves, - the agreement among the proportional mortality curve and each one of the health indicators, infant mortality rate and proportional mortality ratio, in the indication of alteration of the level of health for communities. The statistics, type Kapna, was utilized and these were the findings: (GRAFICO)